Display systems are commonly used to convey information to system observers. Display systems typically include some type of spatial light modulator, such as a Cathode Ray Tube (CRT) or Liquid Crystal Display (LCD) to form a modulated light image. One new type of display system, which has the capability to replace the conventional Cathode Ray Tube (CRT) based display system in many applications, is based on Texas Instruments' Digital Micromirror Device (DMD). The DMD is an integrated circuit that includes a large number of very small mirrors on the surface of the circuit. A typical DMD may have over one million mirrors, each approximately 17 .mu.m across, in a sealed package having a transparent cover over the mirrors. Addressing circuitry in the DMD is used to electrostatically rotate each mirror +/-10.degree. about a hinge axis. The rotated position of the mirror determines the direction incident light will be deflected from the surface of the mirror.
In a typical DMD-based display system, a projection lamp generates a beam of light which is focused onto the surface of the DMD. The incident beam of light generally strikes the surface of the DMD along a path which is 20.degree. from normal to the surface of the DMD. Mirrors which are rotated to a first "on" position reflect the incident light along a path which is normal to the surface of the DMD. Mirrors which are rotated in the opposite "off" direction, reflect light along a path which is 40.degree. from normal to the surface of the DMD and 60.degree. away from the incident light beam.
A projection lens is used to capture the light which has been reflected by the DMD along a path normal to the surface of the DMD. The projection lens focuses this light onto a viewing screen. Each mirror has a one-to-one relationship with a portion of the viewing screen such that for each mirror that is rotated to the "on" position, there is a corresponding bright spot on the viewing screen. The bright spots collectively form an image which may be interpreted by a viewer.
Realistic images require many intensity levels to represent realistically life-like shading and contouring. However, modern versions of the DMD are only designed to operate in either the on position, in which all of the light incident on the mirror is reflected onto the viewing screen, or in the off position, in which none of the incident light is reflected onto the viewing screen. Therefore, time based integration methods are used to create images which have multiple intensity levels. Typical video signals are transmitted as a series of video frames, or images, each frame representing the complete image at a given point in time. Time based integration is implemented by breaking each image frame into a series of subframes. Individually, each subframe is a single-intensity version of the desired image and does not represent the entire image accurately. But, because the human eye integrates a series of instantaneous images, a series of subframes may be created which will appear, to the human eye, to be a single image with multiple intensity levels.
Multiple beams of colored light are used to generate a full-color image. For example, the output of three separate image display systems, one with a red light source, one with a green light source, and one with a blue light source, may be combined to create a full-color image. Alternatively, a single image display system sequentially may use three light sources to generate a full-color image. Once again, the integration properties of the human eye are relied upon to blend the three monochromatic images of a color-serial display system into a single full-color image.